As electronics applications and also microelectromechanical systems (MEMS) shrink in size, research is conducted in order to reduce both footprint and thickness of the electronic components and/or MEMS employed for the various electronics and MEMS applications. There are several reasons for the desire and/or need to reduce the size of the components. In order to achieve a desired physical effect at a given scale, the component needs to have the appropriate size and proportion. For example, reducing a lateral size of a movable element of an acceleration sense may also lead to a reduced mass of the movable element. In order to maintain a desired sensitivity of the acceleration sensor, the stiffness of a suspension of the movable element needs to be reduced, which may require a reduction of the thickness of the suspension mechanism. Simply stated, a reduction of the size of an electronic structure or an MEMS structure typically may involve a reduction of size in all three dimensions in order to maintain the proportions and thus a desired behavior of the component.
From an economical point of view, a size reduction means that more integrated circuits or MEMS devices may fit on a wafer of a given size, thus leading to reduced manufacturing costs per circuit or device.
Some MEMS devices require not only processing at a front surface of the wafer, but also a processing from a back surface of the wafer. Typically, a major part of the MEMS structure is formed at the front surface so that one or more cavities are formed from the back surface all the way through the wafer to the front surface, in order to facilitate the manufacturing steps that need to be performed from the back surface. The one or more cavities may be formed by means of various etching processes, such as wet etching processes or dry etching processes. With wet etching processes typically only relatively small aspect ratios for the cavities can be achieved, i.e., in order to reach a desired depth, the cavities need to be relatively wide at the back surface. Hence, the MEMS structures cannot be placed too close to each other, which results in a waste of wafer estate.
Dry etching techniques, on the other hand, yield high aspect ratios, but are relatively slow and therefore expensive. In particular, the equipment that is needed for dry etching is typically expensive and if one batch takes more than one full day, a large number of dry etching equipment is needed when a desired capacity or throughput is to be reached.
Another aspect that may need to be considered especially in connection with thin wafers is that some techniques for wafer thinning, in particular mechanical techniques such as grinding, can only be used down to a certain minimal wafer thickness. Beneath this minimal wafer thickness mechanical wafer thinning techniques bear a high risk of damaging the wafer and/or the MEMS structures formed at the (front) surface of the wafer.